Flash spinning polycyclopentene

ABSTRACT

A process for flash spinning polycyclopentene that has a number average molecular weight of at least 10,000 to 100,000 and an end of melting range of 250 to 330 ° C. in a spin agent of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons and all having atmospheric boiling points less than 150 ° C.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to plexifilamentary fibers and microcellular and ultramicrocellular foams that are flash-spun from polycyclopentene and a spin agent.

[0003] 2. Description of the Related Art

[0004] Flash-spinning strands of plexifilamentary film-fibrils from polymer in a solution or a dispersion is known in the art. For example, U.S. Pat. No. 3,227,784 to Blades et al., assigned to E. I. du Pont de Nemours & Company, Wilmington, Del. (“DuPont”) describes a process for flash spinning. A polymer in solution is forwarded continuously to a spin orifice at a temperature above the boiling point of the spin agent and at autogenous pressure or greater. This solution is passed to a pressure let-down chamber, where the pressure decreases below the cloud point pressure for the solution thereby causing phase separation. The resulting two-phase dispersion of a solvent-rich phase in a polymer-rich phase is discharged, i.e., flash-spun into a zone of lower temperature and substantially lower pressure to generate a strand of plexifilamentary material.

[0005] A large-scale application for flash spinning as described for instance in U.S. Pat. No. 3,851,023 to Brethauer et al. has been primarily directed to the manufacture of polyolefin plexifilaments, especially of polyethylene and polypropylene. Therefore, it was desirable to develop flash spinning processes for different polymers, particularly those having properties not available with polyethylene and polypropylene.

[0006] U.S. Pat. No. 5,866,663 to Brookhart et al. (Brookhart) discloses polymerization of cyclopentene using nickel and palladium catalysts which has yielded new polycyclopentenes (comprising substantially cis-1, 3-cyclopentene units) which have a crystalline form that differs from that of the highly isotactic (90% or more) polycyclopentenes produced with certain metallocene catalysts, such as zirconium. Polycyclopentenes prepared with zirconium metallocene catalysts have low number average molecular weights (M_(n)≦2000). However, these new polycyclopentenes have weight average molecular weights (Mw) as high as 251,000 and broad melting point transitions with end-of-melting point temperatures ranging from 241 to 330° C.

[0007] Brookhart generally discloses flash spinning of polycyclopentene at column 63, lines 47-54, however, no specifics of a process are provided. For example, there are certain spin agents that are known in the art for flash spinning polyethylene such as n-pentane, cyclopentane, dichloromethane, and 1,1,2-trichloro-2, 2-difluoroethane (HCFC-122). However, these spin agents were not suitable for flash spinning polycyclopentene. The spin agents did not dissolve polycyclopentene, even at pressures as high as 4500 psig (30,923 kPa) and temperatures as high as about 290° C.

SUMMARY OF THE INVENTION

[0008] This invention is a process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polymer which comprises flash spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising 5 to 35 weight percent synthetic fiber-forming polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 260° C. and 330° C. and a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.

[0009] This invention is a process for the preparation of foam fibers from synthetic fiber-forming polymer which comprises flash spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising at least 40 weight percent of fiber-forming polycyclopentene or copolymers thereof and a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.

[0010] This invention is also the spin fluid of polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 260° C. and 300° C. and a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The following definitions are provided to aid in reading and understanding the invention.

[0012] “Plexifilamentary” means a three-dimensional integral network of a multitude of thin, ribbon-like, film-fibril elements of random length and having a mean film thickness of less than about 4 micrometers with a median fibril width of less than about 25 micrometers. In plexifilamentary structures, the film-fibril elements are generally coextensively aligned with the longitudinal axis of the structure and they intermittently unite and separate at irregular intervals in various places throughout the length, width, and thickness of the structure to form a continuous three-dimensional network.

[0013] “Spin agent” as used herein means the solvent that dissolves the polycyclopentene. Primary spin agent refers to solvent when used alone or as the major constituent of a mixture of spin agents. Co-spin agent refers to a solvent when used as a minor constituent of a mixture of spin agents.

[0014] “Spin fluid” as used herein means the solution comprising the polycyclopentene, the primary spin agent and any co-spin agent and additives that may be present. Unless noted otherwise, the term weight percent (wt %) as used herein to describe the composition of a spin fluid refers to the percentage by weight based on the total weight of the spin fluid.

[0015] “Cloud-point pressure” as used herein, means the pressure at which a single-phase liquid solution starts to phase separate into a polymer-rich/spin agent-rich two-phase liquid/liquid dispersion. However, at temperatures above the critical point, there cannot be any liquid phase present and therefore a single phase supercritical solution phase separates into a polymer-rich/spin agent-rich, two-phase gaseous dispersion.

[0016] Because polycyclopentene is the highest melting hydrocarbon polymer that has been flash-spun to date, flash-spun plexifilaments of polycyclopentene can find wide use in high temperature applications such as, for example, steam sterilization, high temperature filtration, protective garments, etc. Therefore, it was desirable to develop flash spinning processes for these new polycyclopentenes, particularly in view of their desirable properties that make them suitable for flash spinning.

[0017] The new polycyclopentene made with alpha-diimine Ni-based catalysts have 50/60% isotacticity that provides the desired lower melting points that were not achievable with polycyclopentene made using Zr metallocene catalysts. Generally, the typical metallocene catalysts produce low molecular weight, high melting point polycyclopentene, while the Ni catalysts make high molecular weight and lower melting point. The Ni catalysts make flash spinning of polycyclopentene possible because only they have been found to provide the suitable combination of melting point and molecular weight ranges.

[0018] The process of this invention for flash-spinning plexifilaments from polycyclopentene and a spin agent operates under conditions of elevated temperature and pressure. In general, for flash spinning, a polymeric starting material is not soluble in the selected spin agent under normal temperature and pressure conditions, but forms a solution at certain elevated temperatures and pressures. The generally known spin agents were not suitable for flash spinning polycyclopentene because they did not dissolve polycyclopentene, even at pressures as high as 4500 psig (30,923 kPa) and temperatures as high as about 290° C. Suitable primary spin agents include 6 to 9 carbon unsubstituted cycloalkanes such as cyclohexane, cycloheptane, and cyclooctane and 6 to 9 carbon alkyl-substituted cycloalkanes, such as methylcyclohexane, dimethylcyclohexane and trimethylcyclohexane. It is preferred that the spin agents have atmospheric boiling points less than 150 C. Cyclohexane has been found to be a preferred spin agent for flash spinning polycyclopentene. The primary spin agents can be used alone or if the solvent power is too high (such as with toluene and xylene) they can be used with a co-spin agent for raising the cloud point pressure, for example hydrofluorocarbons, hydrofluoroethers, perfluorocarbons, hydrochlorofluorocarbons, chlorocarbons, and saturated hydrocarbons. Preferably, the cloud point pressure at the flash spinning temperature is between 800 and 4000 psig (5412 and 27,476 kPa) and more preferably 1000 to 2500 psig (6791 to 17,133 kPa).

[0019] The morphology of fiber strands obtained in a flash-spinning process is greatly influenced by the spin agent, the concentration of the polymer in the spin fluid, and spin conditions. To obtain desired plexifilamentary fibers, polymer concentration is kept relatively low (e.g. less than about 35 weight percent, but at least 5 weight percent) and with spin pressures slightly below the cloud point pressure. This likewise applies to the flash spinning of polycylopentene.

[0020] Well-fibrillated plexifilaments can be obtained when the spin temperature used is between the critical temperature of the spin agent and within 40° C. of the critical temperature, and when the spin pressure is slightly below the cloud point pressure. When the spin pressure is much greater than the cloud point pressure of the spin fluid, coarse plexifilamentary “yarn-like” strands are usually obtained. As the spin pressure is gradually decreased, the average distance between the tie points of the fibrils of the strands generally becomes shorter while the fibrils become progressively finer. When the spin pressure approaches the cloud point pressure of the spin fluid, very fine fibrils are normally obtained, and the distance between the tie points becomes very short. As the spin pressure is further reduced below the cloud point pressure, the distance between tie points becomes longer. Well-fibrillated plexifilaments, which are most suitable for sheet formation, can be generally obtained when spin pressures are slightly below the cloud point pressures. Spin pressures that are too much lower than the cloud point pressure of the spin fluid typically results in a relatively coarse fiber structure. In some cases, well-fibrillated plexifilaments can be obtained even at spin pressures slightly higher than the cloud point pressure of the spin fluid.

[0021] Microcellular and ultramicrocellular foam fibers are usually prepared using strong solvents as spin agents at relatively high polymer concentrations (e.g. between about 40 to 70 weight percent) and at spin pressures that are slightly above the cloud point (or bubble point). The aforementioned aromatic solvents are examples of strong solvents. Flash-spinning of olefin polymers to produce microcellular and ultra-microcellular foam products from polymer solutions is disclosed in U.S. Pat. No. 3,227,664 to Blades et al. and 3,584,090 to Parrish (assigned to DuPont). In many cases, the cloud points of solutions used for spinning microcellular and ultramicrocellular foams are so low that they do not occur until the bubble points are reached. The bubble points are those points that lie on the vapor pressure curve for the solution. In most cases, the actual temperatures and pressures used for spinning plexifilaments are higher than those used for foams, although that is not always the case.

[0022] Microcellular foam fibers may be obtained rather than plexifilaments, even at spinning pressures slightly below the cloud point pressure of the solution. Nucleating agents, such as fused silica and kaolin, may be added to the spin fluid to facilitate spin agent flashing and to obtain foams having uniform small-sized cells (ultramicrocellular foams). Ultramicrocellular foams can also be obtained by using spin temperatures that are greater than a temperature that is 45° C. less than the critical temperature of the spin agent. At these high temperatures, the spin agent undergoes self-nucleation (homogeneous nucleation).

[0023] Microcellular and ultramicrocellular foams can be obtained in a collapsed form, a fully inflated form, or in a partially inflated form. For many polymer/solvent systems, microcellular and ultramicrocellular foams tend to collapse after exiting the spinning orifice as the spin agent vapor condenses inside the cells and/or diffuses out of the cells. To obtain low density inflated foams, inflating agents are usually added to the spin liquid. Inflating agents to be used should have a permeability coefficient for diffusion through the cell walls that is less than that of air so that the agent can stay inside the cells for a long period of time while allowing air to diffuse into the cells to keep the cells inflated. Osmotic pressure will cause air to diffuse into the cells. Suitable inflating agents that can be used include low boiling temperature partially halogenated hydrocarbons or halocarbons such as hydrochlorofluorocarbons, hydrofluorocarbons, hydrofluoroethers, chlorofluorocarbons, perfluorocarbons, and other halogenated compounds.

[0024] Microcellular and ultramicrocellular foam fibers are normally spun from a round cross section spin orifice. However, an annular die similar to the ones used for blown films can be used to make microcellular foam sheets.

[0025] As-spun ultramicrocellular foam fibers can be post-inflated by immersing them in a solvent containing dissolved inflatants. Inflatants will diffuse into the cells due to the plasticizing action of the solvent. Once dried, the inflatants will stay inside the cells and air will diffuse into the cells due to osmotic pressure to keep the ultramicrocellular foams inflated.

[0026] Microcellular foams have densities between 0.005 and 0.50 g/cc. Their cells are generally of a polyhedral shape and their average cell size is less than about 300 micrometers, and is preferably less than about 150 micrometers. Their cell walls are typically less than about 3 micrometers thick, and they are typically less than about 2 micrometers in thickness. Ultramicrocellular foams are typically more uniform and of smaller size than microcellular foams. Typical ultramicrocellular foams have an average cell size of less than 50 micrometers and the cell wall thickness is less than 1 micrometer. As used herein, the term “foams” is meant to include both microcellular and ultramicrocellular foams. Foams of polycyclopentene can be used in insulation, cushioning, etc.

[0027] Plexifilamentary pulps of polycyclopentene can be produced by disc refining flash-spun plexifilaments as disclosed in U.S. Pat. No. 4,608,089 to Gale et al. (assigned to DuPont). Alternatively, such pulps can be prepared directly from polymer solutions by flash spinning using a device similar to the one disclosed in U.S. Pat. No. 5,279,776 to Shah. These pulps are plexifilamentary in nature and they can have a three dimensional network structure. However, the pulp fibers are relatively short in length and have small dimensions in the transverse direction. The average fiber length is less than about 5 millimeters, and is preferably less than 2 millimeters. The average pulp fibril width is less than about 200 micrometers, and is preferably less than 50 micrometers. The pulp fibers have a relatively high surface area (greater than 1 m²/g).

[0028] The polycyclopentene polymer can be prepared as described in U.S. Pat. No. 5,866,663 to Brookhart et al. Unless noted otherwise or it is clear from the context, herein polymer refers to polycyclopentene and copolymers thereof. The polymerizations are catalyzed by selected transition metal compounds that sometimes require co-catalysts as initiators. The process conditions for polymerizing cyclopentene can be varied as was done here to provide polycyclopentene particularly suited for flash spinning. Cyclopentene is available in varying degrees of purity and it is desirable to use the highest purity cyclopentene in order to achieve higher polymer yields based on the number of monomer turnovers per catalyst and to achieve higher molecular weights. The polymerization can be performed in neat cyclopentene, but can also be performed in solution which can provide an increase the polymer yield and narrower melting point ranges. Also, when the solution was used the molecular weights were higher.

[0029] Generally, polycyclopentenes having higher molecular weights and higher melting points are desirable in order to achieve plexifilaments having acceptable physical properties. However, if the molecular weight or melting point is too high, the polymer does not yield acceptable flash-spun product. If the end melting point (measured as described below) is too high, the polymer does not dissolve well in cyclohexane and therefore spins poorly. If the end melting point is too low, the polymer also spins poorly, possibly due to slow or low development of crystallinity. Flash-spun products having acceptable properties were obtained using polycyclopentene having an end melting point between about 260° C. and 330° C. and a peak melting point between about 220° C. to 290° C. and having a number-average molecular weight in the range of 10,000 to 100,000 and preferably, 15,000 to about 70,000 and more preferably in the range of 20,000 to 50,000. If the end melting points are equivalent for different polymers, generally increasing the peak melting point will improve the tensile properties of the flash-spun plexifilaments. If the peak and end melting points are equivalent, then molecular weight begins to play a larger role in the tensile properties, with higher molecular weights yielding higher tensile properties.

[0030] The catalyst used in the polymerization controls the molecular weight and melting point range. The polymer melting point can also be adjusted by varying the polymerization temperature, with higher temperatures yielding lower melting points. The relative concentrations of the cyclopentene and catalyst also affect the melting point and molecular weight. In general, the process variables can be adjusted to obtain polymer having the desired molecular weight and melting point. The main variable is the choice of catalyst followed by the choice of initiators and solvents.

[0031] Useful catalysts, initiators, and solvents are disclosed in U.S. Pat. No. 5,852,145 to McLain et al., International Publication Number WO 99/50320, and International Publication Number WO 00/22007. The preferred catalyst for preparing polycyclopentene suitable for flash-spinning is [bis(2,4,6trimethylphenylimino)acenaphthene]nickel(II) bromide, also referred to herein as [(2,4,6-Me₃PhN)₂An]NiBr₂ and having the following chemical structure:

[0032] Following are other alpha-diimine Ni-based catalysts suitable for use in this invention:

[0033] [2,3-bis(2-chloro-6-methylphenylimino)butane]nickel(II) bromide [(2,6-ClMePhN)₂(CCH₃)₂]NiBr₂

[0034] [bis(2,6-dichloro-4-methoxyphenylimino)acenaphthene]nickel(II) bromide [(2,6-Cl₂-4-OMePhN)₂An]NiBr₂

[0035] [anti-bis(2-isopropyl-6-methylphenylimino)norborane]nickel(II) bromide [anti-(2,6-iPrMePhN)₂NB]NiBr₂

[anti-bis(2-isopropyl-6-methylphenylimino)acenaphthene]nickel(II) bromide [anti-(2,6-iPrMePhN)₂An]NiBr₂

[0036] The polymerization is initiated by contacting the catalyst with alkylaluminum cocatalysts, including aluminoxanes, alkylaluminum chlorides, and trialkylaluminums in combination with suitable Lewis acids that contain or generate non-coordinating anions. Aluminoxanes, such as methylaluminoxane or hydrocarbon-soluble modified methylaluminoxane, are oligomeric materials prepared from trialkylaluminums. Methylaluminoxane is prepared from trimethylaluminum and has the general formula (MeAlO)_(n). Longer alkyl groups can be introduced by using the corresponding trialkylaluminums, which renders it soluble in hydrocarbons. Other aluminoxane derivatives may also be used such as alkylchloraluminoxanes.

[0037] To obtain higher molecular weight polymer and higher polymer yields, the polymerization can be conducted with specific initiators in certain solvents. The preferred initiators are alkylaluminum chlorides and trialkylaluminums in combination with suitable Lewis acids that contain or generate non-coordinating anions. More preferred are ethylaluminum dichloride and triethylaluminum combined with tris (pentafluorophenyl)borane, and most preferred is triethylaluminum combined with tris(pentafluorophenyl)borane.

[0038] The preferred solvents for conducting the polymerization are non-reactive, saturated hydrocarbon and chlorinated hydrocarbon solvents. More preferred are cyclohexane, decahydronaphthalene (Decalin®), tetrachloroethylene, and 1,2,4-trichlorobenzene. Most preferred is 1,2,4-trichlorobenzene. The preferred solvents can result in either lower or higher yields, and the melting point may suffer as well, unless the proper initiator is used. The correct choice of solvent and initiator, which can be determined by simple experimentation, will avoid these difficulties. For example, the use of 1,2,4-trichlorobenzene solvent with triethylaluminum and tris(pentafluorophenyl)borane co-initiators leads to high yields of polymer with the melting point in the preferred range for flash spinning.

Test Methods

[0039] Gas chromatography (GC) was used to analyze cyclopentene monomer to monitor the removal of impurities during purification. GC analysis was performed on Hewlett-Packard gas chromatographs using a 30 m×0.53 mm HP-Plot Al₂O₃ column (#19095P-S23). The samples were injected neat or in heptane solution depending on the injector volume. The temperature program was 150° C. (10 min), 3° C./min to 200° C., 200° C. (15 min).

[0040] Polymer melting point was determined by Differential Scanning Calorimetry at a heating rate of 10° C./minute. Values are reported for the second heating scan of a heat-cool-heat cycle. The subject polymers have relatively broad melting transitions and therefore the melting point is reported both as the peak of the melting endotherm and as the end melting point. The end melting point is measured at the high temperature end of the melting endotherm as the point at which the DSC signal returns to the original (extrapolated) baseline.

[0041] Melt index was measured according to ASTM D1238 at 300° C. and a weight of 8.4 kg and reported in units of flow rate as decigrams per minute (dg/min).

[0042] Molecular weights were measured using gel permeation chromatography (GPC). GPC was performed in 1,2,4trichlorobenzene at 135° C. using a broad molecular weight distribution linear polyethylene standard (Mn (number average molecular weight)=18,300 and M_(w) (weight average molecular weight)=53,100) using a Waters 150C liquid chromatograph equipped with Showdex columns AT-806MS and a Mirian-1A infrared detector.

[0043] The apparatus and procedure for determining the cloud point pressures of the polycyclopentene/spin agent combination are those described in U.S. Pat. No. 5,147,586 to Shin et al.

[0044] Prior to denier measurement and tensile testing, each of the plexifilamentary strands was tensioned by hanging a 40 gm weight for three minutes to remove bends and waviness.

[0045] Tenacity and elongation of the flash-spun strand were determined with an Instron tensile-testing machine. The strands were conditioned and tested at 70° F. (21° C.) and 65% relative humidity. The strands were twisted to 10 turns per inch and mounted in the jaws of the Instron Tester. A two-inch gauge length was used with an initial elongation rate of 4 inches per minute. The tenacity at break is recorded in grams per denier (gpd). The elongation at break is recorded as a percentage of the two-inch gauge length of the sample. Modulus corresponds to the slope of the stress/strain curve and is expressed in units of gpd.

Preparation of Polycyclopentene Polymers

[0046] In the procedures described below, all air-sensitive chemicals and reactions were handled inside nitrogen-purged glove boxes unless noted otherwise. Anhydrous ethylaluminum dichloride (EtAlCl₂) and triethylaluminum (Et₃Al) were obtained from Aldrich (Milwaukee, Wis.). Tris(pentafluorophenyl)borane, B(C₆F₅)₃, was obtained from Boulder Scientific (Boulder, Colo.) and used without further purification.

Cyclopentene Purification

[0047] Cyclopentene (99.8 wt %, obtained from Fluka, Switzerland) was distilled over triflic acid to remove trace ionizable unsaturated impurities and over sodium under nitrogen to remove water, peroxides, and cyclopentadiene.

[0048] Cyclopentene (97.4 wt %, 2.0 wt % cyclopentane, obtained from Nippon Zeon (NZ), Japan) was purified in large batches. It was treated with 5 Å molecular sieves to remove linear unsaturated impurities. GC analysis was used to monitor the complete removal of 1,3-pentadienes as the major linear impurities. The cyclopentene was passed through a column of basic alumina to decompose the peroxides and distilled over sodium under nitrogen.

[0049] An alternate procedure was developed to improve the purity of NZ cyclopentene. The NZ cyclopentene was treated with 5 Å molecular sieves to remove linear unsaturated impurities. The cyclopentene was passed through a column of Amberlyst XN-1010 ion-exchange resin to remove trace ionizable unsaturated impurities. The cyclopentene was distilled over sodium under nitrogen to give high-purity (HP) cyclopentene.

Polymerization Procedure

[0050] The polymerization of cyclopentene particularly suited for flash spinning was performed inside nitrogen-purged glove boxes in dry laboratory bottles equipped with stirring bars (Teflone® polytetrafluoroethylene) poly(ethylene-co-tetrafluoroethylene) pouring rings, and melamine caps lined with Teflon® polytetrafluoroethylene for chemical and thermal resistance. The reaction mixtures were stirred during initiation and until the amount of precipitated polymer was too high to maintain agitation, then transferred to a roller mill if necessary. The polymerization mixtures never remained homogeneous, but precipitated or gelled to varying degrees. The reaction mixtures were quenched using acetylacetone or 8-hydroxyquinoline to discharge the color of active catalyst. The latter formed yellow-green adducts with the nickel and aluminum residues, which were removed by washing with methanol. After work-up, the polymers were dried at 70-90° C. in a vacuum oven under nitrogen purge to determine yield, coated with 0.5 wt % Irganox® 1010 thermal stabilizer using acetone, and redried at 120-140° C. before characterization. The polymers that were flash-spun in these examples were also coated with 0.5 wt % Irganox® 1010.

[0051] Polymer A, used in Example 1, was prepared by mixing [(2,4,6-Me₃PhN)₂An]NiBr₂ (32 mg, 0.050 mmole) with Fluka cyclopentene (44 mL, 34 g, 500 mmol, 10,000 equiv.) and chilling the mixture to below 0° C. The polymerization was initiated by adding EtAlCl₂ (5 mL, 1.0 M in hexanes, 5 mmol, 100 equiv.) to give a dark red-purple solution. After stirring overnight, polymer had precipitated from the solution. The bottle was transferred to a roller mill for agitation. After 6 days, the mixture had solidified. The polymerization was quenched by mixing with 5 wt % acetylacetone in 50 mL cyclohexane. The polymer was washed in turn with fresh cyclohexane, 50 wt % aqueous HCl in methanol (50 mL), and 5 wt % aqueous HCl in methanol (50 mL). The polymer was filtered off and washed 3 times with methanol to give colorless filtrates. The polymer weighed 15.17 g (4400 monomer turnovers per Ni), had a melt index of 19.9 (dg/min) a glass transition temperature (T_(g)) of 95° C., peak melting temperature [T_(m) (peak)] of 227° C., and an end melting temperature [T_(m) (end)] of 282° C.

[0052] Polymer B, used in Example 2, was prepared by polymerization of 31 wt % cyclopentene in tetrachloroethylene to obtain a higher yield of polymer having a higher molecular weight and a lower melting temperature than Polymer A. [(2,4,6-Me₃PhN)₂An]NiBr₂ was mixed with NZ cyclopentene (22 mL, 17 g, 250 mmol, 10,000 equiv.) and tetrachloroethylene (50 mL) and the polymerization was initiated by adding EtAlCl₂ (2.5 mL, 1.0 M in hexanes, 2.5 mmol, 100 equiv.). After 7 days, the solution was very thick. The polymerization was quenched by mixing with 8-hydroxyquinoline (1.21 g, 8.4 mmol, 340 equiv.) in petroleum ether. The polymer was washed with methanol and filtered several times until the filtrates were colorless. The polymer weighed 12.33 g (7200 monomer turnovers per Ni) and had a melt index of 7.2 dg/min, M_(n) of 24,100, M_(w) of 58,700, T_(g) of 99° C., T_(m) (peak) of 226° C., and T_(m) (end) of 263° C.

[0053] Polymer C, used in Example 3, was prepared by polymerization of 33 wt % cyclopentene in Decalin® to obtain polymer having a higher molecular weight than Polymers A and B. [(2,4,6-Me₃PhN)₂An]NiBr₂ (361 mg, 0.569 mmol) was mixed with NZ cyclopentene (440 mL, 341 g, 5 mol, 10,000 equiv.) and 900 mL Decalin®. The polymerization was initiated by adding EtAlCl₂ (50 mL, 1.0 M in pentane, 50 mmol, 100 equiv.) and transferred immediately to a roller mill. After 4 days, the solids reached their maximum level and polymer gel was apparent. The polymerization was continued for additional time without any apparent change. After 2 months, the reaction mixture was quenched by mixing with 8-hydroxyquinoline (24.5 g, 169 mmol, 300 equiv.). The polymer was dispersed in a blender (nitrogen-purged motor) with 1.7 L methanol and washed three times with 1 L methanol until the filtrates were colorless. The polymer weighed 109.75 g (2830 monomer turnovers per Ni) and had a melt index of 2.3 dg/min, M_(n) of 34,600, M_(w) of 140,000, T_(g) of 100° C.; T_(m) (peak) of 246° C., and T_(m) (end) of 283° C.

[0054] Polymer D, used in Example 4, was prepared by polymerization of neat high purity (HP) cyclopentene to obtain polymer having a higher molecular weight than Polymer A. [(2,4,6-Me₃PhN)₂An]NiBr₂ (32 mg, 0.050 mmol) was mixed with HP cyclopentene (44 mL, 34 g, 500 mmol, 10,000 equiv.) and the polymerization was initiated by adding EtAlCl₂ (5 mL, 1.0 M in hexanes, 5 mmol, 100 equiv.). After 7 days, the mixture had solidified. The polymerization was quenched by mixing with 8-hydroxyquinoline (2.47 g, 17 mmol, 340 equiv.) in cyclohexane. The polymer was washed in a blender (nitrogen-purged motor) with methanol and filtered several times until the filtrates were colorless. The polymer was washed three times with methanol. The polymer weighed 13.76 g (4040 monomer turnovers per Ni), had a melt index of 7.0 dg/min, a M_(n) of 30,300, a M_(w) of 61,900, T_(g) of 96° C.; T_(m) (peak) of 238° C., and T_(m) (end) of 280° C.

[0055] Polymer E, used in Example 5, was prepared using high purity cyclopentene and triethylaluminum combined with tris (pentafluorophenyl)borane as co-initiators to obtain a higher molecular weight than Polymer D. [(2,4,6Me₃PhN)₂An]NiBr₂ (32 mg, 0.050 mmol) was mixed with HP cyclopentene (44 mL, 34 g, 500 mmol, 10,000 equiv.). Addition of Et₃Al (0.158 mL, 1.9 M in toluene, 0.300 mmol, 6.0 equiv.) gave a purple solution. Addition of B(C₆F₅)₃ (0.156 g, 0.305 mol, 6.0 equiv.) turned the solution dark. After stirring overnight, polymer had precipitated from the solution. After 4 days, the mixture had solidified. After 7 days, the polymerization was quenched by mixing with 8-hydroxyquinoline (0.23 g, 1.6 mmol, 32 equiv.) in cyclohexane. The polymer was dispersed in a blender (nitrogen-purged motor) with methanol and filtered several times until the filtrates were colorless. The polymer was filtered and washed three times with methanol. The polymer weighed 18.42 g (5400 monomer turnovers per Ni), had a melt index of 4.5 dg/min, a M_(n) of 32,100, a M_(w) of 64,500, a T_(g) of 98° C., T_(m) (peak) of 228° C., and T_(m) (end) of 280° C.

[0056] Polymer F, used in Example 6, was prepared under more dilute conditions than Polymer E to obtain a higher melting point. [(2,4,6-Me₃PhN)₂An]NiBr₂ (16 mg, 0.025 mmol) was mixed with HP cyclopentene (44 mL, 34 g, 500 mmol, 20,000 equiv.) and adding Et₃Al (0.079 mL, 1.9 M in toluene, 0.15 mmol, 6.0 equiv.) to obtain a light purple suspension. Addition of B(C₆F₅)₃ (0.077 g, 0.15 mol, 6.0 equiv.) gave a deep red-purple solution. After several hours, polymer had precipitated from the solution. After three days, the bottle was transferred to a roller mill. After 7 days, the polymer was a wet powdery solid. The polymerization was quenched by mixing with 8-hydroxyquinoline (0.12 g, 0.83 mmol, 33 equiv.) in petroleum ether. The polymer was dispersed in a blender (nitrogen-purged motor) with methanol and filtered to give a yellow-green filtrate. The polymer was washed three times with methanol to give colorless filtrates. The polymer weighed 9.02 g (5300 monomer turnovers per Ni), had a melt index of 1.8 dg/min, a M_(n) of 29,300, a M_(w) of 59,300, a T_(g) of 100° C., T_(m) (peak) of 239° C., and T_(m) (end) of 288° C.

[0057] Polymer G, used in Examples 7 and 8, was prepared by polymerizing 40 wt % cyclopentene in 1,2,4-trichlorobenzene (TCB) using triethylaluminum combined with tris (pentafluorophenyl)borane as co-initiators to obtain a higher molecular weight than Polymer E or F. A solution was prepared from NZ cyclopentene (160 mL, 124 g, 1.82 mol, 10,000 equiv.) and 240 mL TCB. [(2,4,6-Me₃PhN)₂An]NiBr₂ (115 mg, 0.181 mmol) was mixed with 120 mL of the solution. Addition of Et₃Al (0.60 mL, 1.9 M in toluene, 1.1 mmol, 6.3 equiv.) turned the orange-brown solution to dark purple. Addition of B(C₆F₅)₃ (0.56 g, 1.1 mol, 6.0 equiv.) turned the solution dark. After stirring for 1.5 hours, the reaction mixture was diluted with the remaining solution. After 5 days, the solution had set into a dark purple gel. After 10 days, it had formed a hard gel. The polymerization was quenched by mixing the gel with 8-hydroxyquinoline (0.84 g, 5.8 mmol, 32 equiv.) in toluene. The purple color quickly discharged to give a yellow-green mixture. The polymer was dispersed in a blender (nitrogen-purged motor) with 250 mL toluene and extracted by diluting with 250 mL methanol. The polymer was filtered off and washed three times with methanol; the final filtrate was colorless. The polymer weighed 87.5 g (7100 monomer turnovers per Ni), had a melt index of 0.98 dg/min, a M_(n) of 45,300, a M_(w) of 90,700, a T_(g) of 101° C., T_(m) (peak) of 240° C., and T_(m) (end) of 276° C.

EXAMPLES Test Apparatus for Examples 1-7

[0058] The apparatus used in the Examples is described in U.S. Pat. No. 5,147,586 to Shin et al.

[0059] The apparatus described above was charged with pellets of a polycyclopentene polymer and cyclohexane spin agent. High-pressure water was used to drive the pistons to generate a mixing pressure of approximately 2000 psig (8170 kPa). The polymer and spin agent were then heated to a mixing temperature of 250° C. and held at that temperature for 30 minutes, during which time the pistons were used to alternately establish a differential pressure of about 200 psi (1276 kPa) or higher between the two cylinders so as to repeatedly force the polymer and spin agent through the mixing channel from one cylinder to the other to provide mixing and to effect formation of a spin fluid. In order to simulate a pressure letdown chamber, the pressure of the spin fluid was reduced to a desired spinning pressure just prior to spinning. This was accomplished by opening a valve between the spin cell and a much larger tank of high-pressure water (“the accumulator”) held at the desired spinning pressure. The spinneret orifice is opened as rapidly as possible after the opening of the valve between the spin cell and the accumulator. This generally takes about one second. This is intended to simulate the letdown chamber effect that is used in larger scale spinning operations. The resultant flash-spun product was collected in a stainless steel open mesh screen basket. The pressure recorded just before the spinneret using a computer during spinning is entered as the spin pressure.

[0060] It is noted that pressures may be expressed as psig (pounds per square inch gage) which is approximately 15 psi less than psia (pound per square inch absolute). The unit psi is considered the same as psia. For converting to SI units, 1 psi=6.9 kPa.

Examples 1-7

[0061] These examples demonstrate flash spinning of the polycyclopentenes prepared above, the polycyclopentene polymers having a range of peak and end melting temperatures, melt index, and molecular weight.

[0062] Spin fluids were prepared, as described above, having a concentration of polycyclopentene of 30 wt %, based on the total weight of the spin fluid. The spinneret orifice had a diameter of 30 mils (0.762 mm) with a 30-mil land and with no spin tunnel. Cyclohexane was used as the spin agent. The spin fluids were flash-spun using the method described above and spin conditions given in Table 1 to obtain well-fibrillated plexifilaments having acceptable properties. TABLE 1 Spin Conditions and Plexifilament Properties for Flash-Spun Polycyclopentene Polycyclopentene Polymer Properties Tm (° C.) MI Example/Polymer Peak End Dg/min Mn Mw 1/A 227 282 19.9 — — 2/B 226 263 7.2 24,100 58,700 3/C 246 283 2.3 34,600 140,000  4/D 238 280 7.0 30,300 61,900 5/E 228 280 4.5 32,100 64,500 6/F 239 288 1.8 29,300 59,300 7/G 240 276 0.98 45,300 90,700 Spinning Conditions Accum P Properties (psig) Spin P Temp Ten Mod E Example (kPa (psig) (° C.) Den gpd gpd % 1 1200 1100 250 407 0.87 7.34 32.2 (8170) (7481) 2 1200 1100 250 473 0.60 5.42 33.9 (8170) (7481) 3 1200 1050 250 484 1.37 8.68 33.0 (8170) (7136) 4 1200 1075 250 466 1.05 8.44 30.1 (8170) (7308) 5 1100 1000 250 413 0.89 7.36 29.8 (7481) (6791) 6 1200 1050 250 442 1.59 10.1 35.1 (8170) (7136) 7 1200 1000 248 477 1.14 2.06 49.2 (8170) (6791)

Example 8

[0063] This example demonstrates flash spinning of polycyclopentene ultramicrocellular foam. Polycyclopentene Polymer G was used to prepare a spin fluid containing 50 weight percent polycyclopentene in cyclohexane spin agent. Cab-O-Sil N70-TS colloidal silica was added to the spin fluid at 1.0 weight percent, based on polymer. The spin fluid was prepared by mixing the polymer, spin agent, and colloidal silica at 150 to 245° C. for about 25 minutes at a back pressure of 2000 psi (13790 kPa) and a differential pressure of about 1300 psi (8963 kPa). The spin fluid was then cooled to a spin temperature of 210° C. while mixing. Cooling took place over a period of about 25 minutes for a total mixing time of 50 minutes. The spinning apparatus was the same as that used in Examples 1-7 except that the spinneret orifice had a diameter of 15 mils (0.381 mm). The spin fluid was flash spun at 210° C., an accumulator pressure of 750 psig (5068 kPa), and a spin pressure of 400-425 psig (2654-2827 kPa) to provide acceptable ultramicrocellular foam fiber. 

What is claimed is:
 1. A process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polymer which comprises flash spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) 5 to 35 weight percent based on the weight of the spin fluid of synthetic fiber-forming polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 260° C. and 330° C. (b) a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.
 2. The process of claim 1, wherein the plexifilamentary film-fibril strands have a tenacity of at least 1 gram per denier.
 3. A process for the preparation of foam fibers from synthetic fiber-forming polymer which comprises flash spinning at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure, a spin fluid comprising (a) 40 to 70 weight percent based on the weight of the spin fluid of fiber-forming polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 250° C. and 330° C., and (b) a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.
 4. A spin fluid comprising: (a) 5 to 35 weight percent based on the weight of the spin fluid of synthetic fiber-forming polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 260° C. and 330° C. and (b) a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.
 5. A spin fluid comprising: (a) 40 to 70 weight percent based on the weight of the spin fluid of synthetic fiber-forming polycyclopentene or copolymers thereof having a number average molecular weight of 10,0000 to 100,000 and an end melting point between 250° C. and 330° C. and (b) a primary spin agent having an atmospheric boiling point less than 150° C. selected from the group consisting of 6 to 9 carbon cycloalkanes, 6 to 9 carbon alkyl-substituted cycloalkanes and alkyl-substituted aromatic hydrocarbons.
 6. The process according to claims 1-5, wherein the spin agent of 6 to 9 carbon cycloalkane is selected from the group consisting of cyclohexane, cycloheptane, and cyclooctane and the spin agent of 6 to 9 carbon alkyl-substituted cycloalkane is selected from the group consisting of methylcyclohexane, dimethylcyclohexane and trimethylcyclohexane and the spin agent of alkyl-substituted aromatic solvent is selected from the group consisting of xylene and toluene.
 7. The spin fluid of either of claims 1-5, further comprising a co-spin agent for raising the cloud point pressure selected from the group consisting of hydrofluorocarbons, hydrofluoroethers, perfluorocarbons, hydrochlorofluorocarbons, chlorocarbons, and saturated hydrocarbons.
 8. Foam, comprising polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 250° C. and 330° C.
 9. Pulp, comprising polycyclopentene or copolymers thereof having a number average molecular weight of 10,000 to 100,000 and an end melting point between 260° C. and 330° C. 